• spring高级源码50讲-43-50(spring续)

    其它

    43) FactoryBean

    演示 - FactoryBean
    代码参考
    package com.itheima.a43;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;

@ComponentScan
public class A43 {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A43.class);

        Bean1 bean1 = (Bean1) context.getBean("bean1");
        Bean1 bean2 = (Bean1) context.getBean("bean1");
        Bean1 bean3 = (Bean1) context.getBean("bean1");
        System.out.println(bean1);
        System.out.println(bean2);
        System.out.println(bean3);

        System.out.println(context.getBean(Bean1.class));

        System.out.println(context.getBean(Bean1FactoryBean.class));
        System.out.println(context.getBean("&bean1"));

        context.close();

        /*
            学到了什么: 一个在 Spring 发展阶段中重要, 但目前已经很鸡肋的接口 FactoryBean 的使用要点
            说它鸡肋有两点:
                1. 它的作用是用制造创建过程较为复杂的产品, 如 SqlSessionFactory, 但 @Bean 已具备等价功能
                2. 使用上较为古怪, 一不留神就会用错
                    a. 被 FactoryBean 创建的产品
                        - 会认为创建、依赖注入、Aware 接口回调、前初始化这些都是 FactoryBean 的职责, 这些流程都不会走
                        - 唯有后初始化的流程会走, 也就是产品可以被代理增强
                        - 单例的产品不会存储于 BeanFactory 的 singletonObjects 成员中, 而是另一个 factoryBeanObjectCache 成员中
                    b. 按名字去获取时, 拿到的是产品对象, 名字前面加 & 获取的是工厂对象
            就说恶心不?

            但目前此接口的实现仍被大量使用, 想被全面废弃很难
         */
    }

}


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    package com.itheima.a43;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.annotation.Autowired;

import javax.annotation.PostConstruct;

public class Bean1 implements BeanFactoryAware {
    private static final Logger log = LoggerFactory.getLogger(Bean1.class);

    private Bean2 bean2;

    @Autowired
    public void setBean2(Bean2 bean2) {
        log.debug("setBean2({})", bean2);
        this.bean2 = bean2;
    }

    public Bean2 getBean2() {
        return bean2;
    }

    @PostConstruct
    public void init() {
        log.debug("init");
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        log.debug("setBeanFactory({})", beanFactory);
    }
}


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    package com.itheima.a43;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.stereotype.Component;

@Component("bean1")
public class Bean1FactoryBean implements FactoryBean<Bean1> {

    private static final Logger log = LoggerFactory.getLogger(Bean1FactoryBean.class);

    // 决定了根据【类型】获取或依赖注入能否成功
    @Override
    public Class<?> getObjectType() {
        return Bean1.class;
    }

    // 决定了 getObject() 方法被调用一次还是多次
    @Override
    public boolean isSingleton() {
        return true;
    }

    @Override
    public Bean1 getObject() throws Exception {
        Bean1 bean1 = new Bean1();
        log.debug("create bean: {}", bean1);
        return bean1;
    }
}


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    收获💡
    1. 它的作用是用制造创建过程较为复杂的产品, 如 SqlSessionFactory, 但 @Bean 已具备等价功能
    2. 使用上较为古怪, 一不留神就会用错
      1. 被 FactoryBean 创建的产品
        • 会认为创建、依赖注入、Aware 接口回调、前初始化这些都是 FactoryBean 的职责, 这些流程都不会走
        • 唯有后初始化的流程会走, 也就是产品可以被代理增强
        • 单例的产品不会存储于 BeanFactory 的 singletonObjects 成员中, 而是另一个 factoryBeanObjectCache 成员中
      2. 按名字去获取时, 拿到的是产品对象, 名字前面加 & 获取的是工厂对象

    44) @Indexed 原理

    真实项目中，只需要加入以下依赖即可

    <dependency>
    <groupId>org.springframeworkgroupId>
    <artifactId>spring-context-indexerartifactId>
    <optional>trueoptional>
dependency>

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    演示 - @Indexed
    代码参考
    package com.itheima.a44;

import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.ClassPathBeanDefinitionScanner;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;

/*
    做这个试验前, 先在 target/classes 创建 META-INF/spring.components, 内容为

    com.itheima.a44.Bean1=org.springframework.stereotype.Component
    com.itheima.a44.Bean2=org.springframework.stereotype.Component

    做完实现建议删除, 避免影响其它组件扫描的结果

    真实项目中, 这个步骤可以自动完成, 加入以下依赖
    
        org.springframework
        spring-context-indexer
        true
    
 */
public class A44 {
    public static void main(String[] args) throws IOException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
        // 组件扫描的核心类
        ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(beanFactory);

        scanner.scan(A44.class.getPackageName());

        for (String name : beanFactory.getBeanDefinitionNames()) {
            System.out.println(name);
        }

        /*
            学到了什么
                a. @Indexed 的原理, 在编译时就根据 @Indexed 生成 META-INF/spring.components 文件
                扫描时
                1. 如果发现 META-INF/spring.components 存在, 以它为准加载 bean definition
                2. 否则, 会遍历包下所有 class 资源 (包括 jar 内的)
         */
    }
}


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    收获💡
    1. 在编译时就根据 @Indexed 生成 META-INF/spring.components 文件
    2. 扫描时
      • 如果发现 META-INF/spring.components 存在, 以它为准加载 bean definition
      • 否则, 会遍历包下所有 class 资源 (包括 jar 内的)
    3. 解决的问题，在编译期就找到 @Component 组件，节省运行期间扫描 @Component 的时间

    45) 代理进一步理解

    演示 - 代理
    代码参考
    package com.itheima.a45;

import org.springframework.aop.framework.Advised;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

import java.lang.reflect.Method;

@SpringBootApplication
public class A45 {

    public static void main(String[] args) throws Exception {
        ConfigurableApplicationContext context = SpringApplication.run(A45.class, args);

        Bean1 proxy = context.getBean(Bean1.class);



        /*
            1.演示 spring 代理的设计特点
                依赖注入和初始化影响的是原始对象
                代理与目标是两个对象，二者成员变量并不共用数据
         */
//        showProxyAndTarget(proxy);
//
//        System.out.println(">>>>>>>>>>>>>>>>>>>");
//        System.out.println(proxy.getBean2());
//        System.out.println(proxy.isInitialized());

        /*
            2.演示 static 方法、final 方法、private 方法均无法增强
         */

        proxy.m1();
        proxy.m2();
        proxy.m3();
        Method m4 = Bean1.class.getDeclaredMethod("m1");
        m4.setAccessible(true);
        m4.invoke(proxy);

        context.close();
    }


    public static void showProxyAndTarget(Bean1 proxy) throws Exception {
        System.out.println(">>>>> 代理中的成员变量");
        System.out.println("\tinitialized=" + proxy.initialized);
        System.out.println("\tbean2=" + proxy.bean2);

        if (proxy instanceof Advised advised) {
            System.out.println(">>>>> 目标中的成员变量");
            Bean1 target = (Bean1) advised.getTargetSource().getTarget();
            System.out.println("\tinitialized=" + target.initialized);
            System.out.println("\tbean2=" + target.bean2);
        }
    }

}


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    收获💡

    1. spring 代理的设计特点

      • 依赖注入和初始化影响的是原始对象

        • 因此 cglib 不能用 MethodProxy.invokeSuper()

      • 代理与目标是两个对象，二者成员变量并不共用数据

    2. static 方法、final 方法、private 方法均无法增强

      • 进一步理解代理增强基于方法重写

    46) @Value 装配底层

    按类型装配的步骤
    1. 查看需要的类型是否为 Optional，是，则进行封装（非延迟），否则向下走
    2. 查看需要的类型是否为 ObjectFactory 或 ObjectProvider，是，则进行封装（延迟），否则向下走
    3. 查看需要的类型（成员或参数）上是否用 @Lazy 修饰，是，则返回代理，否则向下走
    4. 解析 @Value 的值
      1. 如果需要的值是字符串，先解析 ${ }，再解析 #{ }
      2. 不是字符串，需要用 TypeConverter 转换
    5. 看需要的类型是否为 Stream、Array、Collection、Map，是，则按集合处理，否则向下走
    6. 在 BeanFactory 的 resolvableDependencies 中找有没有类型合适的对象注入，没有向下走
    7. 在 BeanFactory 及父工厂中找类型匹配的 bean 进行筛选，筛选时会考虑 @Qualifier 及泛型
    8. 结果个数为 0 抛出 NoSuchBeanDefinitionException 异常
    9. 如果结果 > 1，再根据 @Primary 进行筛选
    10. 如果结果仍 > 1，再根据成员名或变量名进行筛选
    11. 结果仍 > 1，抛出 NoUniqueBeanDefinitionException 异常
    演示 - @Value 装配过程
    代码参考
    package com.itheima.a46;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.beans.factory.config.BeanExpressionContext;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ContextAnnotationAutowireCandidateResolver;
import org.springframework.stereotype.Component;

import java.lang.reflect.Field;

// 本章节作为第四讲的延续
@Configuration
@SuppressWarnings("all")
public class A46 {

    public static void main(String[] args) throws Exception {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A46.class);
        DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();

        ContextAnnotationAutowireCandidateResolver resolver = new ContextAnnotationAutowireCandidateResolver();
        resolver.setBeanFactory(beanFactory);

//        test1(context, resolver, Bean1.class.getDeclaredField("home"));
//        test2(context, resolver, Bean1.class.getDeclaredField("age"));
//        test3(context, resolver, Bean2.class.getDeclaredField("bean3"));
        test3(context, resolver, Bean4.class.getDeclaredField("value"));
    }

    private static void test3(AnnotationConfigApplicationContext context, ContextAnnotationAutowireCandidateResolver resolver, Field field) {
        DependencyDescriptor dd1 = new DependencyDescriptor(field, false);
        // 获取 @Value 的内容
        String value = resolver.getSuggestedValue(dd1).toString();
        System.out.println(value);

        // 解析 ${}
        value = context.getEnvironment().resolvePlaceholders(value);
        System.out.println(value);
        System.out.println(value.getClass());

        // 解析 #{} @bean3
        Object bean3 = context.getBeanFactory().getBeanExpressionResolver().evaluate(value, new BeanExpressionContext(context.getBeanFactory(), null));

        // 类型转换
        Object result = context.getBeanFactory().getTypeConverter().convertIfNecessary(bean3, dd1.getDependencyType());
        System.out.println(result);
    }

    private static void test2(AnnotationConfigApplicationContext context, ContextAnnotationAutowireCandidateResolver resolver, Field field) {
        DependencyDescriptor dd1 = new DependencyDescriptor(field, false);
        // 获取 @Value 的内容
        String value = resolver.getSuggestedValue(dd1).toString();
        System.out.println(value);

        // 解析 ${}
        value = context.getEnvironment().resolvePlaceholders(value);
        System.out.println(value);
        System.out.println(value.getClass());
        Object age = context.getBeanFactory().getTypeConverter().convertIfNecessary(value, dd1.getDependencyType());
        System.out.println(age.getClass());
    }

    private static void test1(AnnotationConfigApplicationContext context, ContextAnnotationAutowireCandidateResolver resolver, Field field) {
        DependencyDescriptor dd1 = new DependencyDescriptor(field, false);
        // 获取 @Value 的内容
        String value = resolver.getSuggestedValue(dd1).toString();
        System.out.println(value);

        // 解析 ${}
        value = context.getEnvironment().resolvePlaceholders(value);
        System.out.println(value);
    }

    public class Bean1 {
        @Value("${JAVA_HOME}")
        private String home;
        @Value("18")
        private int age;
    }

    public class Bean2 {
        @Value("#{@bean3}") // SpringEL       #{SpEL}
        private Bean3 bean3;
    }

    @Component("bean3")
    public class Bean3 {
    }

    static class Bean4 {
        @Value("#{'hello, ' + '${JAVA_HOME}'}")
        private String value;
    }
}


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    收获💡
    1. ContextAnnotationAutowireCandidateResolver 作用之一，获取 @Value 的值
    2. 了解 ${ } 对应的解析器
    3. 了解 #{ } 对应的解析器
    4. TypeConvert 的一项体现

    47) @Autowired 装配底层

    演示 - @Autowired 装配过程
    代码参考
    package com.itheima.a47;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ContextAnnotationAutowireCandidateResolver;
import org.springframework.context.annotation.Lazy;
import org.springframework.core.MethodParameter;
import org.springframework.stereotype.Component;

import java.lang.reflect.Method;
import java.util.Optional;

@Configuration
public class A47_1 {
    public static void main(String[] args) throws NoSuchFieldException, NoSuchMethodException {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A47_1.class);
        DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 1. 根据成员变量的类型注入
        DependencyDescriptor dd1 = new DependencyDescriptor(Bean1.class.getDeclaredField("bean2"), false);
        System.out.println(beanFactory.doResolveDependency(dd1, "bean1", null, null));
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 2. 根据参数的类型注入
        Method setBean2 = Bean1.class.getDeclaredMethod("setBean2", Bean2.class);
        DependencyDescriptor dd2 = new DependencyDescriptor(new MethodParameter(setBean2, 0), false);
        System.out.println(beanFactory.doResolveDependency(dd2, "bean1", null, null));
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 3. 结果包装为 Optional
        DependencyDescriptor dd3 = new DependencyDescriptor(Bean1.class.getDeclaredField("bean3"), false);
        if (dd3.getDependencyType() == Optional.class) {
            dd3.increaseNestingLevel();
            Object result = beanFactory.doResolveDependency(dd3, "bean1", null, null);
            System.out.println(Optional.ofNullable(result));
        }
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 4. 结果包装为 ObjectProvider,ObjectFactory
        DependencyDescriptor dd4 = new DependencyDescriptor(Bean1.class.getDeclaredField("bean4"), false);
        if (dd4.getDependencyType() == ObjectFactory.class) {
            dd4.increaseNestingLevel();
            ObjectFactory objectFactory = new ObjectFactory() {
                @Override
                public Object getObject() throws BeansException {
                    return beanFactory.doResolveDependency(dd4, "bean1", null, null);
                }
            };
            System.out.println(objectFactory.getObject());
        }
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");
        // 5. 对 @Lazy 的处理
        DependencyDescriptor dd5 = new DependencyDescriptor(Bean1.class.getDeclaredField("bean2"), false);
        ContextAnnotationAutowireCandidateResolver resolver = new ContextAnnotationAutowireCandidateResolver();
        resolver.setBeanFactory(beanFactory);
        Object proxy = resolver.getLazyResolutionProxyIfNecessary(dd5, "bean1");
        System.out.println(proxy);
        System.out.println(proxy.getClass());
        /*
            学到了什么
                1. Optional 及 ObjectFactory 对于内嵌类型的处理, 源码参考 ResolvableType
                2. ObjectFactory 懒惰的思想
                3. @Lazy 懒惰的思想
            下一节, 继续学习 doResolveDependency 内部处理
         */
    }

    static class Bean1 {
        @Autowired @Lazy private Bean2 bean2;
        @Autowired public void setBean2(Bean2 bean2) {
            this.bean2 = bean2;
        }
        @Autowired private Optional<Bean2> bean3;
        @Autowired private ObjectFactory<Bean2> bean4;
    }

    @Component("bean2")
    static class Bean2 {
        /*@Override
        public String toString() {
            return super.toString();
        }*/
    }
}


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    package com.itheima.a47;

import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ContextAnnotationAutowireCandidateResolver;
import org.springframework.stereotype.Component;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

@SuppressWarnings("all")
@Configuration
public class A47_2 {
    public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A47_2.class);
        DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> 1. 数组类型");
        testArray(beanFactory);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> 2. List 类型");
        testList(beanFactory);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> 3. applicationContext");
        testApplicationContext(beanFactory);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> 4. 泛型");
        testGeneric(beanFactory);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> 5. @Qualifier");
        testQualifier(beanFactory);
        /*
            学到了什么
                1. 如何获取数组元素类型
                2. Spring 如何获取泛型中的类型
                3. 特殊对象的处理, 如 ApplicationContext, 并注意 Map 取值时的类型匹配问题 (另见  TestMap)
                4. 谁来进行泛型匹配 (另见 TestGeneric)
                5. 谁来处理 @Qualifier
                6. 刚开始都只是按名字处理, 等候选者确定了, 才会创建实例
         */
    }

    private static void testQualifier(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {
        DependencyDescriptor dd5 = new DependencyDescriptor(Target.class.getDeclaredField("service"), true);
        Class<?> type = dd5.getDependencyType();
        ContextAnnotationAutowireCandidateResolver resolver = new ContextAnnotationAutowireCandidateResolver();
        resolver.setBeanFactory(beanFactory);
        for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, type)) {
            BeanDefinition bd = beanFactory.getMergedBeanDefinition(name);
            //                                                             @Qualifier("service2")
            if (resolver.isAutowireCandidate(new BeanDefinitionHolder(bd,name), dd5)) {
                System.out.println(name);
                System.out.println(dd5.resolveCandidate(name, type, beanFactory));
            }
        }
    }
    private static void testGeneric(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {
        DependencyDescriptor dd4 = new DependencyDescriptor(Target.class.getDeclaredField("dao"), true);
        Class<?> type = dd4.getDependencyType();
        ContextAnnotationAutowireCandidateResolver resolver = new ContextAnnotationAutowireCandidateResolver();
        resolver.setBeanFactory(beanFactory);
        for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, type)) {
            BeanDefinition bd = beanFactory.getMergedBeanDefinition(name);
            // 对比 BeanDefinition 与 DependencyDescriptor 的泛型是否匹配
            if (resolver.isAutowireCandidate(new BeanDefinitionHolder(bd,name), dd4)) {
                System.out.println(name);
                System.out.println(dd4.resolveCandidate(name, type, beanFactory));
            }
        }
    }
    private static void testApplicationContext(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException, IllegalAccessException {
        DependencyDescriptor dd3 = new DependencyDescriptor(Target.class.getDeclaredField("applicationContext"), true);

        Field resolvableDependencies = DefaultListableBeanFactory.class.getDeclaredField("resolvableDependencies");
        resolvableDependencies.setAccessible(true);
        Map<Class<?>, Object> dependencies = (Map<Class<?>, Object>) resolvableDependencies.get(beanFactory);
//        dependencies.forEach((k, v) -> {
//            System.out.println("key:" + k + " value: " + v);
//        });
        for (Map.Entry<Class<?>, Object> entry : dependencies.entrySet()) {
            // 左边类型                      右边类型
            if (entry.getKey().isAssignableFrom(dd3.getDependencyType())) {
                System.out.println(entry.getValue());
                break;
            }
        }
    }
    private static void testList(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {
        DependencyDescriptor dd2 = new DependencyDescriptor(Target.class.getDeclaredField("serviceList"), true);
        if (dd2.getDependencyType() == List.class) {
            Class<?> resolve = dd2.getResolvableType().getGeneric().resolve();
            System.out.println(resolve);
            List<Object> list = new ArrayList<>();
            String[] names = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, resolve);
            for (String name : names) {
                Object bean = dd2.resolveCandidate(name, resolve, beanFactory);
                list.add(bean);
            }
            System.out.println(list);
        }
    }
    private static void testArray(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {
        DependencyDescriptor dd1 = new DependencyDescriptor(Target.class.getDeclaredField("serviceArray"), true);
        if (dd1.getDependencyType().isArray()) {
            Class<?> componentType = dd1.getDependencyType().getComponentType();
            System.out.println(componentType);
            String[] names = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, componentType);
            List<Object> beans = new ArrayList<>();
            for (String name : names) {
                System.out.println(name);
                Object bean = dd1.resolveCandidate(name, componentType, beanFactory);
                beans.add(bean);
            }
            Object array = beanFactory.getTypeConverter().convertIfNecessary(beans, dd1.getDependencyType());
            System.out.println(array);
        }
    }
    static class Target {
        @Autowired private Service[] serviceArray;
        @Autowired private List<Service> serviceList;
        @Autowired private ConfigurableApplicationContext applicationContext;
        @Autowired private Dao<Teacher> dao;
        @Autowired @Qualifier("service2") private Service service;
    }
    interface Dao<T> {

    }
    @Component("dao1") static class Dao1 implements Dao<Student> {
    }
    @Component("dao2") static class Dao2 implements Dao<Teacher> {
    }

    static class Student {

    }

    static class Teacher {

    }

    interface Service {

    }

    @Component("service1")
    static class Service1 implements Service {

    }

    @Component("service2")
    static class Service2 implements Service {

    }

    @Component("service3")
    static class Service3 implements Service {

    }
}


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    package com.itheima.a47;

import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;

@Configuration
public class A47_3 {
    public static void main(String[] args) throws NoSuchFieldException {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A47_3.class);
        DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();
        testPrimary(beanFactory);
        testDefault(beanFactory);

        /*
            学到了什么
                1. @Primary 的处理, 其中 @Primary 会在 @Bean 解析或组件扫描时被解析 (另见 TestPrimary)
                2. 最后的防线, 通过属性或参数名匹配
         */
    }

    private static void testDefault(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {
        DependencyDescriptor dd = new DependencyDescriptor(Target2.class.getDeclaredField("service3"), false);
        Class<?> type = dd.getDependencyType();
        for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, type)) {
            if(name.equals(dd.getDependencyName())) {
                System.out.println(name);
            }
        }
    }

    private static void testPrimary(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {
        DependencyDescriptor dd = new DependencyDescriptor(Target1.class.getDeclaredField("service"), false);
        Class<?> type = dd.getDependencyType();
        for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, type)) {
            if (beanFactory.getMergedBeanDefinition(name).isPrimary()) {
                System.out.println(name);
            }
        }
    }

    static class Target1 {
        @Autowired private Service service;
    }

    static class Target2 {
        @Autowired private Service service3;
    }

    interface Service {

    }
    @Component("service1") static class Service1 implements Service {

    }
    @Component("service2") static class Service2 implements Service {

    }
    @Component("service3") static class Service3 implements Service {

    }
}


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    收获💡
    1. @Autowired 本质上是根据成员变量或方法参数的类型进行装配
    2. 如果待装配类型是 Optional，需要根据 Optional 泛型找到 bean，再封装为 Optional 对象装配
    3. 如果待装配的类型是 ObjectFactory，需要根据 ObjectFactory 泛型创建 ObjectFactory 对象装配
      • 此方法可以延迟 bean 的获取
    4. 如果待装配的成员变量或方法参数上用 @Lazy 标注，会创建代理对象装配
      • 此方法可以延迟真实 bean 的获取
      • 被装配的代理不作为 bean
    5. 如果待装配类型是数组，需要获取数组元素类型，根据此类型找到多个 bean 进行装配
    6. 如果待装配类型是 Collection 或其子接口，需要获取 Collection 泛型，根据此类型找到多个 bean
    7. 如果待装配类型是 ApplicationContext 等特殊类型
      • 会在 BeanFactory 的 resolvableDependencies 成员按类型查找装配
      • resolvableDependencies 是 map 集合，key 是特殊类型，value 是其对应对象
      • 不能直接根据 key 进行查找，而是用 isAssignableFrom 逐一尝试右边类型是否可以被赋值给左边的 key 类型
    8. 如果待装配类型有泛型参数
      • 需要利用 ContextAnnotationAutowireCandidateResolver 按泛型参数类型筛选
    9. 如果待装配类型有 @Qualifier
      • 需要利用 ContextAnnotationAutowireCandidateResolver 按注解提供的 bean 名称筛选
    10. 有 @Primary 标注的 @Component 或 @Bean 的处理
    11. 与成员变量名或方法参数名同名 bean 的处理

    48) 事件监听器

    演示 - 事件监听器
    代码参考
    package com.itheima.a48;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.stereotype.Component;

// 事件解耦例子
@Configuration
public class A48_1 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A48_1.class);
        context.getBean(MyService.class).doBusiness();
        context.close();
    }

    static class MyEvent extends ApplicationEvent {
        public MyEvent(Object source) {
            super(source);
        }
    }

    @Component
    static class MyService {
        private static final Logger log = LoggerFactory.getLogger(MyService.class);
        @Autowired
        private ApplicationEventPublisher publisher; // applicationContext
        public void doBusiness() {
            log.debug("主线业务");
            // 主线业务完成后需要做一些支线业务，下面是问题代码
            publisher.publishEvent(new MyEvent("MyService.doBusiness()"));
        }
    }

//    @Component
    static class SmsApplicationListener implements ApplicationListener<MyEvent> {
        private static final Logger log = LoggerFactory.getLogger(SmsApplicationListener.class);
        @Override
        public void onApplicationEvent(MyEvent event) {
            log.debug("发送短信");
        }
    }

    @Component
    static class EmailApplicationListener implements ApplicationListener<MyEvent> {
        private static final Logger log = LoggerFactory.getLogger(EmailApplicationListener.class);
        @Override
        public void onApplicationEvent(MyEvent event) {
            log.debug("发送邮件");
        }
    }

}

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    package com.itheima.a48;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.EventListener;
import org.springframework.context.event.SimpleApplicationEventMulticaster;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import org.springframework.stereotype.Component;

import java.util.concurrent.ThreadPoolExecutor;

@Configuration
public class A48_2 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A48_2.class);
        context.getBean(MyService.class).doBusiness();
        context.close();
    }

    static class MyEvent extends ApplicationEvent {
        public MyEvent(Object source) {
            super(source);
        }
    }

    @Component
    static class MyService {
        private static final Logger log = LoggerFactory.getLogger(MyService.class);
        @Autowired
        private ApplicationEventPublisher publisher; // applicationContext
        public void doBusiness() {
            log.debug("主线业务");
            // 主线业务完成后需要做一些支线业务，下面是问题代码
            publisher.publishEvent(new MyEvent("MyService.doBusiness()"));
        }
    }

    @Component
    static class SmsService {
        private static final Logger log = LoggerFactory.getLogger(SmsService.class);
        @EventListener
        public void listener(MyEvent myEvent) {
            log.debug("发送短信");
        }
    }

    @Component
    static class EmailService {
        private static final Logger log = LoggerFactory.getLogger(EmailService.class);
        @EventListener
        public void listener(MyEvent myEvent) {
            log.debug("发送邮件");
        }
    }

    @Bean
    public ThreadPoolTaskExecutor executor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(3);
        executor.setMaxPoolSize(10);
        executor.setQueueCapacity(100);
        return executor;
    }

    @Bean
    public SimpleApplicationEventMulticaster applicationEventMulticaster(ThreadPoolTaskExecutor executor) {
        SimpleApplicationEventMulticaster multicaster = new SimpleApplicationEventMulticaster();
        multicaster.setTaskExecutor(executor);
        return multicaster;
    }

}

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    package com.itheima.a48;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.SmartInitializingSingleton;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Method;

@Configuration
public class A48_3 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A48_3.class);
        context.getBean(MyService.class).doBusiness();
        context.close();
    }

    @Bean
    public SmartInitializingSingleton smartInitializingSingleton(ConfigurableApplicationContext context) {
        return () -> {
            for (String name : context.getBeanDefinitionNames()) {
                Object bean = context.getBean(name);
                for (Method method : bean.getClass().getMethods()) {
                    if (method.isAnnotationPresent(MyListener.class)) {
                        context.addApplicationListener((event) -> {
                            System.out.println(event);
                            Class<?> eventType = method.getParameterTypes()[0];// 监听器方法需要的事件类型
                            if (eventType.isAssignableFrom(event.getClass())) {
                                try {
                                    method.invoke(bean, event);
                                } catch (Exception e) {
                                    e.printStackTrace();
                                }
                            }
                        });
                    }
                }
            }
        };
    }

    @Component
    static class MyService {
        private static final Logger log = LoggerFactory.getLogger(MyService.class);
        @Autowired
        private ApplicationEventPublisher publisher; // applicationContext

        public void doBusiness() {
            log.debug("主线业务");
            // 主线业务完成后需要做一些支线业务，下面是问题代码
            publisher.publishEvent(new MyEvent("MyService.doBusiness()"));
        }
    }

    @Component
    static class SmsService {
        private static final Logger log = LoggerFactory.getLogger(SmsService.class);

        @MyListener
        public void listener(MyEvent myEvent) {
            log.debug("发送短信");
        }
    }

    @Component
    static class EmailService {
        private static final Logger log = LoggerFactory.getLogger(EmailService.class);

        @MyListener
        public void listener(MyEvent myEvent) {
            log.debug("发送邮件");
        }
    }

    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.METHOD)
    @interface MyListener {
    }

    static class MyEvent extends ApplicationEvent {
        public MyEvent(Object source) {
            super(source);
        }
    }
}

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    收获💡

    事件监听器的两种方式

    1. 实现 ApplicationListener 接口
      • 根据接口泛型确定事件类型
    2. @EventListener 标注监听方法
      • 根据监听器方法参数确定事件类型
      • 解析时机：在 SmartInitializingSingleton（所有单例初始化完成后），解析每个单例 bean

    49) 事件发布器

    演示 - 事件发布器
    代码参考
    package com.itheima.a49;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.context.event.GenericApplicationListener;
import org.springframework.core.ResolvableType;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import org.springframework.stereotype.Component;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;

@Configuration
public class A49 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A49.class);
        context.getBean(MyService.class).doBusiness();
        context.close();
    }

    static class MyEvent extends ApplicationEvent {
        public MyEvent(Object source) {
            super(source);
        }
    }

    @Component
    static class MyService {
        private static final Logger log = LoggerFactory.getLogger(MyService.class);
        @Autowired
        private ApplicationEventPublisher publisher; // applicationContext

        public void doBusiness() {
            log.debug("主线业务");
            // 主线业务完成后需要做一些支线业务，下面是问题代码
            publisher.publishEvent(new MyEvent("MyService.doBusiness()"));
        }
    }

    @Component
    static class SmsApplicationListener implements ApplicationListener<MyEvent> {
        private static final Logger log = LoggerFactory.getLogger(SmsApplicationListener.class);

        @Override
        public void onApplicationEvent(MyEvent event) {
            log.debug("发送短信");
        }
    }

    @Component
    static class EmailApplicationListener implements ApplicationListener<MyEvent> {
        private static final Logger log = LoggerFactory.getLogger(EmailApplicationListener.class);

        @Override
        public void onApplicationEvent(MyEvent event) {
            log.debug("发送邮件");
        }
    }

    @Bean
    public ThreadPoolTaskExecutor executor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(3);
        executor.setMaxPoolSize(10);
        executor.setQueueCapacity(100);
        return executor;
    }

    @Bean
    public ApplicationEventMulticaster applicationEventMulticaster(ConfigurableApplicationContext context, ThreadPoolTaskExecutor executor) {
        return new AbstractApplicationEventMulticaster() {
            private List<GenericApplicationListener> listeners = new ArrayList<>();

            // 收集监听器
            public void addApplicationListenerBean(String name) {
                ApplicationListener listener = context.getBean(name, ApplicationListener.class);
                System.out.println(listener);
                // 获取该监听器支持的事件类型
                ResolvableType type = ResolvableType.forClass(listener.getClass()).getInterfaces()[0].getGeneric();
                System.out.println(type);

                // 将原始的 listener 封装为支持事件类型检查的 listener
                GenericApplicationListener genericApplicationListener = new GenericApplicationListener() {
                    // 是否支持某事件类型                真实的事件类型
                    public boolean supportsEventType(ResolvableType eventType) {
                        return type.isAssignableFrom(eventType);
                    }

                    public void onApplicationEvent(ApplicationEvent event) {
                        executor.submit(() -> listener.onApplicationEvent(event));
                    }
                };

                listeners.add(genericApplicationListener);
            }

            // 发布事件
            public void multicastEvent(ApplicationEvent event, ResolvableType eventType) {
                for (GenericApplicationListener listener : listeners) {
                    if (listener.supportsEventType(ResolvableType.forClass(event.getClass()))) {
                        listener.onApplicationEvent(event);
                    }
                }
            }
        };
    }

    abstract static class AbstractApplicationEventMulticaster implements ApplicationEventMulticaster {

        @Override
        public void addApplicationListener(ApplicationListener<?> listener) {

        }

        @Override
        public void addApplicationListenerBean(String listenerBeanName) {

        }

        @Override
        public void removeApplicationListener(ApplicationListener<?> listener) {

        }

        @Override
        public void removeApplicationListenerBean(String listenerBeanName) {

        }

        @Override
        public void removeApplicationListeners(Predicate<ApplicationListener<?>> predicate) {

        }

        @Override
        public void removeApplicationListenerBeans(Predicate<String> predicate) {

        }

        @Override
        public void removeAllListeners() {

        }

        @Override
        public void multicastEvent(ApplicationEvent event) {

        }

        @Override
        public void multicastEvent(ApplicationEvent event, ResolvableType eventType) {

        }
    }
}

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    package com.itheima.a49;

import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.context.PayloadApplicationEvent;
import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.context.event.GenericApplicationListener;
import org.springframework.context.support.GenericApplicationContext;
import org.springframework.core.ResolvableType;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;

// 演示事件发布器实现要点
public class TestEventPublisher {
    public static void main(String[] args) {
        GenericApplicationContext context = new GenericApplicationContext();
        context.registerBean("applicationEventMulticaster", MyApplicationEventMulticaster.class);
        context.refresh();

        context.publishEvent(new Object());
        context.publishEvent("aaaa");
        context.publishEvent(new Bean1());
    }

    interface Inter {

    }

    static class Bean1 implements Inter{

    }

    static class MyApplicationEventMulticaster implements ApplicationEventMulticaster {

        private List<ApplicationListener> listeners = new ArrayList<>();

        {
            listeners.add(new GenericApplicationListener() {
                @Override
                public void onApplicationEvent(ApplicationEvent event) {
                    if (event instanceof PayloadApplicationEvent payloadApplicationEvent) {
                        System.out.println(payloadApplicationEvent.getPayload());
                    }
                }

                @Override
                public boolean supportsEventType(ResolvableType eventType) {
                    System.out.println(eventType);
                    // eventType --> PayloadApplicationEvent, PayloadApplicationEvent
                    return (Inter.class.isAssignableFrom(eventType.getGeneric().toClass()));
                }
            });
        }

        @Override
        public void addApplicationListener(ApplicationListener<?> listener) {

        }

        @Override
        public void addApplicationListenerBean(String listenerBeanName) {

        }

        @Override
        public void removeApplicationListener(ApplicationListener<?> listener) {

        }

        @Override
        public void removeApplicationListenerBean(String listenerBeanName) {

        }

        @Override
        public void removeApplicationListeners(Predicate<ApplicationListener<?>> predicate) {

        }

        @Override
        public void removeApplicationListenerBeans(Predicate<String> predicate) {

        }

        @Override
        public void removeAllListeners() {

        }

        @Override
        public void multicastEvent(ApplicationEvent event) {
            multicastEvent(event, null);
        }

        @SuppressWarnings("all")
        @Override
        public void multicastEvent(ApplicationEvent event, ResolvableType eventType) {
            listeners.stream().filter(applicationListener -> {
                        if (eventType == null) {
                            return false;
                        }
                        if (applicationListener instanceof GenericApplicationListener genericApplicationListener) {
                            return genericApplicationListener.supportsEventType(eventType);
                        }
                        return false;
                    })
                    .forEach(applicationListener -> {
                        applicationListener.onApplicationEvent(event);
                    });
        }
    }
}

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    收获💡
     

    事件发布器模拟实现
     

    1. addApplicationListenerBean 负责收集容器中的监听器 
  
      • 监听器会统一转换为 GenericApplicationListener 对象，以支持判断事件类型
       
    2. multicastEvent 遍历监听器集合，发布事件 
  
      • 发布前先通过 GenericApplicationListener.supportsEventType 判断支持该事件类型才发事件
      • 可以利用线程池进行异步发事件优化
       
    3. 如果发送的事件对象不是 ApplicationEvent 类型，Spring 会把它包装为 PayloadApplicationEvent 并用泛型技术解析事件对象的原始类型 
  
      • 视频中未讲解
       
    
                
                    
                

                
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                    原文地址：https://blog.csdn.net/kuangzeng/article/details/132628145
                
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